Section 5 Details and fastenings

5.1.1 This Section contains the general Rule requirements to be complied with for fibre reinforced plastic craft being built under survey. Where detailed requirements are not defined good boat building practices are to be applied. Where different details are to be applied, the Builder is required to provide evidence of satisfactory service experience or acceptable test data.

5.2.1 Details of alignment and building tolerances are to be laid down in the Builder's production plan.

5.2.2 Where details of alignment and building tolerances are not included on the construction plans, or submitted separately for consideration with the plan submission, they may, subject to individual consideration, be agreed locally with the attending Surveyor.

5.2.3 Particular attention is to be given to the accurate alignment of the following:

1. girder abutting single skin bulkhead;

2. girder webs with tank sides;

3. frames with beams;

4. deck/bottom girders with bulkhead stiffeners;

5. tank baffles with floors;

6. longitudinals where broken at tank ends; and

7. transom stiffeners with bottom/deck girders.

5.2.4 For larger craft the hull breakage sight-line is to be progressively monitored during the construction of the craft and is to form part of the quality control documentation. The production plan is to identify maximum breakage limits dependent upon the size of the craft.

5.2.5 The production plan is to identify allowable tolerances for the alignment of the primary structural components.

5.2.6 To ensure efficient load transmission intercostal, single skin bulkheads are to be aligned to within half the thickness of the thinner bulkhead. In the case of sandwich construction the tolerance requirements will be individually considered dependent upon the sandwich panel dimensions and the construction of the continuous member. In general, the webs of the intercostal sandwich panel member are to be aligned to within 5 mm. Where poor alignment is identified, additional boundary bonding reinforcements are to be applied as agreed with the attending Surveyor. Such deviations and details of the remedial action taken are to be recorded in the Builder's quality control documentation.

5.2.7 To ensure efficient transmission of shear loads, the alignment tolerance of intercostal `top hat' stiffener webs is, in general, to be within half of the web thickness. Where poor alignment is identified, additional reinforcements are, in general, to be incorporated into the stiffener webs as agreed with the attending Surveyor. Such deviations and details of the remedial action taken are to be recorded in the Builder's quality control documentation.

5.3.1 Continuity of all primary structural members is to be maintained, as required by the Rules, and abrupt changes of section are to be avoided. Both primary and secondary stiffening members are to be continuous unless otherwise agreed with LR.

5.3.2 Special consideration will be given to the intersection of longitudinal and transverse members. In general the ratio between the depths of the intersecting members is to be 2:1. The shallower member is to be continuous under the supporting members.

5.3.3 Alternative proposals to the requirements given in Pt 8, Ch 2, 5.3 Continuity 5.3.2 will be subject to special consideration in conjunction with the submission of details for maintaining the continuity of reinforcements at intersections in both directions. Where stiffeners are of similar dimensions the primary member is to be continuous. In general the section modulus of the continuous material is to be maintained.

5.4.1 All openings are to have well rounded corners and are to be supported on all sides. Cut edges of openings are to be sealed to prevent the ingress of moisture.

5.4.2 All hatch openings are to be supported by a system of transverse and longitudinal stiffeners, the details of which are to be submitted for approval.

5.4.3 The requirements for closing arrangements and outfit are given in Pt 3, Ch 4 Closing Arrangements and Outfit.

5.4.4 All deck openings are to have corner radii as specified in Pt 8, Ch 3, 8.12 Deck openings.

5.4.5 For details of sealing the edges of openings and sandwich panels, see Pt 8, Ch 2, 5.10 Exposed edges.

5.5.1 The details of all through bolted structural connections are to be indicated on the relevant construction plans submitted for approval. The design of the joint is to be suitable for its intended purpose with a sufficient number of bolts to satisfactorily close the joint.

5.5.2 Tank tops may be bolted down provided the bolt spacing does not exceed 8d _b, where d _bis the bolt diameter. A joint, seal or stop water is to be fitted, as necessary, to meet the required integrity.

5.5.3 In general, large headed bolts or large diameter thick washers are to be used to prevent localised crushing damage during tightening.

5.5.4 Where mechanical fastenings are used, the torque is to be indicated on the plans submitted for approval.

5.5.5 Bolting arrangements are, in general, to be in accordance with Pt 8, Ch 2, 5.5 Through bolting and bolted connections, Pt 8, Ch 2, 5.6 Through hull fittings, Pt 8, Ch 2, 5.7 Backing bars and tapping plates and Pt 8, Ch 2, 5.8 Fastenings. In FRP sandwich construction, inserts of a material capable of resisting crushing are to be fitted in accordance with Pt 8, Ch 2, 4.3 Inserts.

5.5.6 The diameter of a fastening is not to be less than the thickness of the thinner component being fastened, with a minimum diameter of 6 mm, excepting window frames where the minimum diameter may be 5 mm.

5.5.7 Bolted connections are, in general, to be bonded along all mating surfaces using an accepted structural adhesive, applied in accordance with the manufacturer's requirements. Where connections rely solely on the shear resistance of the connecting bolts the spacing is not to exceed 3d _b, where d _b is the diameter of the bolt. In areas where subsequent access will either be limited or not possible, self locking nuts are to be provided.

5.5.8 In general, all structural, bolted connections are to use reeled lines of bolts in accordance with the requirements given in Table 2.5.1 Bolt pitch requirements in bonded and bolted connections.

5.5.9 All structural, single line, bolted connections without adhesive bondings are to be in accordance with the requirements given in Table 4.1.1 Bolt pitch requirements for structural connections in Pt 3, Ch 4.

5.5.10 Care is to be taken to avoid distortion of the frame when window frames are bolted into the structure of the craft. Where necessary, uneven surfaces are to be locally built up to the satisfaction of the attending Surveyor.

5.5.11 Where a restricted service notation of G1 or G2 is applicable the requirements given in this Section will be specially considered dependent upon the sea states for which the craft is designed.

5.5.12 Bolt holes are to be drilled, without undue pressure at break through, having a diametric tolerance of two per cent of the bolt diameter. Where bolted connections are to be made watertight the hole is to be sealed with resin and allowed to cure before the bolt is inserted.

5.5.13 In areas of high stress or where unusual bolting configurations are proposed, testing on the basis of equivalence with the above Rules may be required.

5.6.1 Where fittings penetrate the hull envelope, care is to be taken to seal the hull laminate with resin or other suitable compound, see Pt 8, Ch 2, 5.10 Exposed edges.

5.6.2 The areas in way of penetrations for fittings in sandwich construction are, in general, to comply with the requirements of Pt 8, Ch 2, 4.3 Inserts. Where the requirements cannot be complied with, the core is to be replaced locally with a solid core or very high density foam core with compressive properties commensurate with the loads imposed by the securing arrangements, see Pt 8, Ch 2, 5.8 Fastenings 5.8.2. The exposed edges of such openings are to be sealed watertight, see Pt 8, Ch 3, 3.10 Shell openings.

5.6.3 All bolted fittings are to be bedded down using a suitable mastic, details of which are to be indicated on the submitted plans.

5.7.1 The requirements for backing plates and bars will be individually considered, on the basis of the loading imposed, details of which are to be indicated on the submitted plans.

5.7.2 Metallic plates and bars are to comply with the requirements of Pt 8, Ch 2, 2.1 General 2.1.2 (such as suitable marine grades of stainless steel or aluminium alloys).

5.7.3 Tapping plates may be encapsulated within the laminate, laminated to or bolted to the structure, see also Pt 8, Ch 2, 2.15 Adhesives 2.15.1. Where tapping plate edges or corners are likely to give rise to hard spots or stress concentrations the edges are to be suitably rounded.

5.7.4 Where tapping plates are placed on foam cores the plate is to be mounted on a suitable foundation to prevent the movement of the tapping plate during drilling operations.

5.7.5 Direct calculations regarding the scantlings of tapping plates are to be provided at the plan appraisal stage.

5.8.1 All fastenings are to be of a suitable marine grade. Sizes and specifications are to be indicated on the submitted plans.

5.8.2 In areas where localised crushing of a sandwich core is likely to occur, large diameter washers, compression tubes or inserts or a combination of these are to be adopted.

5.9.1 Laminating is to proceed as a continuous process, as far as practicable, with the minimum of delay between successive plies. Where a secondary bond is to be made it is to be carried out in accordance with the resin manufacturer's recommendation, details of which are to be incorporated in the Builder's quality control documentation. This will, in general, take the form of the area being lightly abraded and wiped with a suitable solvent, which is to be allowed to dry prior to laminating.

5.9.2 Where other than epoxy resins are being used, the first reinforcement is to be of the chopped strand mat type.

5.9.3 Consideration should be given, especially in highly stressed areas, to the application of peel ply materials to obviate contamination of the exposed surface, and thereby reducing the abrading required to obtain a good secondary bond.

5.10.1 The exposed edges of all openings cut in single skin laminate panels are to be suitably sealed. Where such edges are in wet spaces or under water the edges of such openings are to have rounded edges and are to be sealed by two plies of 450g/m² chopped strand mat (or equivalent) reinforcements, see also Pt 8, Ch 3, 3.10 Shell openings.

5.10.2 Exposed edges of openings cut in sandwich panels are to be suitably sealed, see Pt 8, Ch 2, 5.6 Through hull fittings 5.6.2. The cut edges are, in general, to be sealed with a weight of reinforcement not less than that required for the outer skin of the sandwich. Where other than an epoxy resin system is used the first layer of such reinforcement is to be chopped strand mat with a weight not exceeding 450 g/m², see also Pt 8, Ch 3, 3.10 Shell openings.

5.11.1 The details of all joints, the proposed jointing procedure and information regarding tolerancing are to be indicated on the submitted plans.

5.11.2 Joints may be bolted or adhesively bonded, or both. Where joints are bolted, full details of the bolt material, the proposed number and spacing are to be provided. Bolts are to be manufactured from a non-corrosive material or protected against corrosion.

5.12.1 Areas subject to local loads or increased stress are to be suitably reinforced, details of which are to be indicated on the submitted plans, see Pt 8, Ch 3, 3.14 Local reinforcement.

5.12.2 The design of the structure, in way of the attachment of fittings or equipment in sandwich structures, is to be such that the induced loads can be transmitted into the surrounding structure by bending as opposed to shear. The areas are, in general, to take the form of suitably reinforced single skin areas, see Pt 8, Ch 3, 3.14 Local reinforcement, with the additional layers of reinforcement staggered out onto the surrounding inner and outer skins as indicated in Figure 3.3.1 Single skin/sandwich skin intersection detail.

5.13.1 Details of the hull to deck connection, the method of bonding and the tolerances are to be indicated on the submitted plans.

5.13.2 Hull to deck connections should, in general, be bolted and over-bonded. A suitable mastic or sealing compound is to be incorporated within the joint.

5.13.3 The bolting details should be reeled lines of bolts pitched as specified in Table 2.5.1 Bolt pitch requirements in bonded and bolted connections. Suitable large diameter thick washers should be used under both the head and the nut.

5.13.4 Where a mastic is not used, sealing plies are to be applied on the inside of the hull.

5.13.5 The weight of the over-bonding reinforcement is, in general, not to be taken as less than equivalent to the lighter of the component members being connected, and in no case less than equivalent to three plies of 600 g/m² chopped strand mat.

5.13.6 Substantial beam knees are to be provided to maintain structural continuity between the transverse deck and hull stiffening.

5.13.7 The watertight integrity, continuity and strength of the connection is not to be impaired by the attachment of the hull fender.

5.13.8 For guidance details of scantlings required to resist impact loads at deck edge connections see Pt 8, Ch 3, 4.19 Fenders and reinforcement in way for side shell in way of fendering and Pt 8, Ch 3, 3.6 Sheerstrake for sheerstrakes.

5.14.1 Exhaust systems, manufactured from FRP, are to be of the water injected type with a normal operating temperature of 60° - 70°C and a maximum operating temperature of 120°C.

5.14.2 Exhaust pipes, silencers and water separators should be of a Type Approved design, installed strictly in accordance with the manufacturer's requirements.

5.14.3 Where a Type Approved system is not used, the arrangement will be considered on an individual basis. Resins used in the manufacture of exhaust systems are to be of a type approved by LR and are to have good heat and chemical resistance properties with a high deflection temperature under load. A vinylester resin should be used, but a fire retardant polyester resin, having a high heat distortion temperature, will be considered. Test samples may be required dependent upon the proposed arrangement, temperatures and materials.

5.14.4 It is recommended that pigments and additives are not used unless it can be demonstrated that the mechanical properties of the resin system remain unaffected. Resins used are not to show any embrittlement with age.

5.14.5 Special consideration is to be given to post curing of such systems to obtain optimal characteristics.

5.14.6 Due to the weight of water contained within the system, exhaust pipes and fittings are to be efficiently supported.

5.14.7 Exhaust boxes are to be lined with a minimum of two plies of 600g/m² chopped strand mat (or equivalent) using a suitable fire retardant/high temperature resin.

5.14.8 For engineering aspects of exhaust systems reference is to be made to Pt 10, Ch 1, 8.3 Exhaust systems.

5.14.9 National Authority requirements take precedence over the requirements given in this Section.

5.15.1 The provision of permanent ballast is not to adversely affect the surrounding structure.

5.15.2 Where a resin compound is to be poured into a void space, care is to be taken to minimise the generation of heat that may affect the mechanical and weathering characteristics of the structural laminate.

5.15.3 Details of all ballast materials and the proposed method of installation are to be indicated on the submitted plans.

5.16.1 Provision is to be made to drain areas likely to accumulate liquids, details of which are to be indicated on the submitted plans.

5.16.2 The size, shape and position of limber holes are not to affect the structural strength of the stiffening members in which they are fitted. Limber holes are, in general, to be positioned at the quarter span of the stiffener.

5.17.1 The surfaces of integral tanks are to be provided with a barrier to reduce the ingress of liquid. The details of the proposed system are to be indicated on the submitted plans.

5.17.2 Fresh water tanks are to be coated with a non-toxic and non-tainting coat of resin that is recommended by the resin manufacturer for potable water tanks.

5.17.3 The design and arrangement of fuel oil tanks is to be such that there is no exposed horizontal section at the bottom that could be exposed to a fire. Other fire protection arrangements for fuel oil tanks will be specially considered. For details of fire protection requirements see Pt 17 Fire Protection, Detection and Extinction.

5.17.4 Where plywood bulkheads form part of a tank boundary, the surface is to be completely protected against the ingress of moisture with a minimum of 4 mm thickness of laminate to provide an effective fluid barrier, regardless of resin and reinforcement type used.

5.17.5 Where outfit items are to be laminated to the tank surface, the heavy coating of resin is to be applied afterwards and the laminated brackets sealed to prevent the ingress of moisture.

5.17.6 The scantlings of integral fuel oil and water tanks are to be in accordance with Pt 8, Ch 3, 7 Bulkheads and deep tanks. Details regarding sub-division of integral tanks are given in Pt 8, Ch 3, 7.11 Wash plates 7.11.1.

5.17.7 Integral tanks are to be tested in accordance with Pt 8, Ch 3, 7.17 Testing.

5.18.1 Details of materials to be used and the method of installation of reserve buoyancy are to be indicated on the submitted plans.

5.18.2 Where necessary, buoyancy materials are to be over-laminated in situ to prevent the ingress of moisture.

5.19.1 Where the total web depth to thickness ratio requirement in Pt 8, Ch 3, 1.17 Stiffener proportions for buckling of stiffener webs is not complied with, cross linking of the stiffener webs at the Rule depth to thickness ratio is to be provided by the use of shear ties, as indicated in Figure 2.5.1 Arrangement of shear ties (stiffeners).

Figure 2.5.1 Arrangement of shear ties (stiffeners)

5.19.2 Alternative arrangements will be subject to individual consideration in conjunction with submitted direct calculations.